Dolpa , Nepal -LRB- CNN -RRB- -- Ram Bahadur Jafra and his two brothers crouch on a field , picking through blades of grass and staring at the soil . They have traveled five days by foot to a Himalayan meadow at a 4,300 meter elevation deep inside Nepal 's Dolpa district . They came , as tens of thousands do each year , to harvest a highly valuable commodity from the high-altitude soil : the Himalayan caterpillar fungus -- also known as Himalayan Viagra .

Caterpillar fungus , or as it 's called in Tibetan , `` yartsa gunbu , '' meaning `` summer grass , winter worm , '' is a specimen created when a parasitic fungus infects caterpillars underground which , were they not forestalled by the fungus , would produce ghost moths .

After the fungus mummifies the caterpillar underground , it thrusts out of the soil . It 's this tiny protuberance that the harvesters spend weeks each spring searching for .

A hundred or so people crawl across the field in a mulled silence until a sole searcher lets out an excited cry . Dozens rush over to witness , Jafra is the first to arrive .

The woman who has discovered the specimen uses an ice pick to prod the earth and dig a hole about six inches in diameter . She then lifts a clump of earth up and sifts out the specimen . The crowd gossips about its value -- `` it 's small , only 300 rupees ! '' -LRB- about $ 3 -RRB- . A middle man will offer her that amount , then walk it to a market in Tibet and sell it for three times the price .

Jafra explains : `` We pay attention when other people find them . This is our first time coming for the harvest . We 've been here for nearly a week . We have n't found anything , because we do n't know what they look like -- we do n't know what we 're looking for . ''

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Like many others , Ram and his brothers traveled for the harvest betting on hope alone . `` People in our village talked about the money to be earned , so we came , '' he says .

The rumors of riches are not baseless . According to experts , the market value of yartsa gunbu has increased by 900 % between 1997 and 2008 .

One study says 500 grams of top quality yartsa gunbu can sell for up to $ 13,000 in Lhasa , Tibet , or up to $ 26,000 in Shanghai . Average annual income in Nepal 's rural mid-and-far-western hills , where many harvesters live , is just $ 283 , according to the government .

Police in Dolpa expect 40,000 people to migrate to the district this year . The influx of migrant harvesters speaks volumes to the increasing global commodification of yartsa gunbu . Prized in traditional Tibetan and Chinese medicinal practices for its power as an elixir or an aphrodisiac , in recent years commercial dubbing of the product as `` Himalayan Viagra '' has driven up both demand and market value around the world .

But the unprecedented flood of harvesters has observers concerned about the environmental impacts of this informal economic boom .

`` Look at the hills , '' says Gyalpo Thandin , a student in Dolpa , `` they 're all torn up from people digging . By next year they 'll be deserts . ''

Thandin , who was visiting home for the harvest , remembers when the yartsa gunbu season meant local bounty , not commercial competition . `` Just five years ago the numbers were lower , '' he says . `` Every year we see more people come and more grasslands get damaged . People who come hack at the land with tools and leave it to dry out . ''

He says his family 's yaks have died in recent winters due to depleted grass caused by the harvest .

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Environmental protection measures offer some hope . Six years ago , a committee of community leaders in Dolpa instituted a taxation system on harvesters in an effort to control numbers and ensure the local community remained resilient amidst environmental changes .

The committee charges locals 1,000 rupees -LRB- $ 11 -RRB- and outsiders 3,000 rupees -LRB- $ 33 -RRB- to join the harvest . The system is intended to spend the money on environmental protection measures and to subsidize food for villages in the district .

Similar systems exist in harvest areas across the Himalayas . However , some worry the measure is ineffective .

A former committee member who spoke on the condition of anonymity suggests that charging admission to the harvest has only made it seem even more valuable , and as a result , drawn more harvesters . `` The goal of the system was to charge people and therefore limit the number who would want to come for the harvest , but putting a price on the entry might actually be encouraging more people , '' he says .

A leading expert on Himalayan caterpillar fungus , ecologist and geographer Daniel Winkler , believes the future of the harvests is contingent on many factors -- collection intensity , rainfall , and climate change among them .

`` Centuries of collection indicate that caterpillar fungus is a relatively resilient resource , '' he says .

But his research suggests that over-harvesting is contributing to fewer fungal spores being around for the next season . Winkler believes education is the key element to promoting sustainable resource conservation .

`` Knowledge of fungal reproduction ... and -LRB- establishing -RRB- an end-date to the collection season might allow for sufficient spore dispersal to guarantee sustainability , '' he adds .

As communities in Nepal , one of the world 's poorest countries , cope with the economic need and the increasing desire for high-value commodities like yartsa gunbu , conservation efforts will require cooperation between leaders at village , district , and national levels . There is no question this Himalayan `` gold rush '' buoys rural economies . Keeping it around for future generations will be the challenge .

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Caterpillar fungus -- known as Himalayan Viagra -- is prized in traditional medicine

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Thousands of people travel to Nepal 's Dolpa district each year to harvest the caterpillar fungus

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Some locals say the harvesters are damaging hillsides and grasslands

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Expert says education is needed for the harvesting to be sustainable long term